Swirl sign (intracranial hemorrhage)

The swirl sign refers to the non-contrast CT appearance of acute extravasation of blood into a hematoma, for example an intracerebral hemorrhageextradural hematoma or subdural hematoma. It represents unclotted fresh blood which is of lower attenuation than the clotted blood which surrounds it .

It is the corollary of the spot sign on CTA which represents the same phenomenon, but in that case caused by contrast extravasation .